As air travel has increased over the past decades, airport facilities have become more crowded and congested. Minimizing the time between the arrival of an aircraft and its departure to maintain an airline's flight schedule, and also to make a gate or parking location available without delay to an incoming aircraft, has become a high priority in the management of airport ground operations. The safe and efficient ground movement of a large number of aircraft simultaneously into and out of ramp and gate areas has become increasingly important. As airline fuel costs and safety concerns and regulations have increased, the airline industry is beginning to acknowledge that continuing to use an aircraft's main engines to move aircraft during ground operations is no longer the best option. The delays, costs, and other challenges to timely and efficient aircraft pushback from airport terminals associated with the use of tugs and tow vehicles makes this type of aircraft ground movement an unattractive alternative to the use of an aircraft's main engines to move an aircraft on the ground. Restricted use of an aircraft's engines on low power during arrival at or departure from a gate is an additional, although problematic, option. Not only does such engine use consume fuel, it is also burns fuel inefficiently and produces engine exhaust that contains microparticles and other products of incomplete combustion. Operating aircraft engines, moreover, are noisy, and the associated safety hazards of jet blast and engine ingestion in congested gate and ramp areas are significant concerns that cannot be overlooked.
The use of a drive means, such as a motor structure, integrally mounted with a wheel to rotate the wheel of an aircraft has been proposed. Such a structure should ideally operate to replace use of an aircraft's main engines or an external tow vehicle to move an aircraft independently and efficiently on the ground during taxi. U.S. Pat. No. 2,430,163 to Dever; U.S. Pat. No. 3,977,631 to Jenny; U.S. Pat. No. 7,226,018 to Sullivan; and U.S. Pat. No. 7,445,178 to McCoskey et al, for example, describe various drive means concepts and motors intended to drive aircraft during ground operations. None of the foregoing patents, however, suggests a drive mechanism selectively activated by a clutch to transfer torque and actuate a drive system that actuates a drive means only as required during taxi to move an aircraft independently and efficiently on the ground.
U.S. Pat. No. 7,469,858 to Edelson; U.S. Pat. No. 7,891,609 to Cox; U.S. Pat. No. 7,975,960 to Cox; U.S. Pat. No. 8,109,463 to Cox et al; and British Patent No. 2457144, owned in common with the present invention, describe aircraft drive systems that use electric drive motors to power aircraft wheels and move an aircraft on the ground without reliance on aircraft main engines or external vehicles. While the drive means described in these patents and applications can effectively move an aircraft autonomously during ground operations, it is not suggested that the drive means could be driven or actuated by selective clutch activation of a drive system to selectively transfer torque to actuate an electric motor or any other drive means. None of the foregoing art, moreover, recognizes the significant improvements in drive means operating efficiency possible when gearing systems are replaced by clutch-controlled selective activation of a roller traction or other drive system to transfer torque and actuate drive means that move aircraft autonomously during ground operations.
The drive means currently proposed to drive aircraft on the ground typically rely on gearing systems that operate with the drive means to drive an aircraft wheel and, thus, the aircraft. Traction drives, such as that described in U.S. Pat. No. 4,617,838 to Anderson, available from Nastec, Inc. of Cleveland, Ohio, which relies on ball bearings, can be used to replace gears in some contexts. Adapting roller or traction drive systems to replace gearing and/or gear systems in an aircraft drive wheel to actuate drive means that independently drive an aircraft drive wheel has not been suggested, nor has the use of a selectively activatable clutch assembly to selectively transfer torque to activate such roller traction drive or other drive systems been mentioned.
Many types of vehicle clutch assemblies are well known in the art. U.S. Pat. No. 3,075,623 to Lund; U.S. Pat. No. 3,599,767 to Soderquist; and U.S. Pat. No. 7,661,329 to Cali et al, for example, describe clutch assemblies incorporating sprag or pawl elements that may transmit torque between races or rotatable elements depending, in part, on their relative directions of rotation. One way vehicle clutches designed to lock in one direction and allow free rotation in the opposite direction are also available, as are improved selectable one way clutch designs, such as those described in U.S. Pat. No. 6,290,044 to Burgman et al; U.S. Pat. No. 7,980,371 to Joki; and U.S. Pat. No. 8,042,670 to Bartos et al. Various other selectable clutch designs that provide controllable overrunning and coupling functions in automotive automatic transmissions, are described in U.S. Pat. No. 8,079,453 to Kimes and in U.S. Patent Application Publication Nos. US2010/0252384 to Eisengruber; US2011/0233026 to Pawley; and US2013/0277164 to Prout et al. It is not suggested that any of the foregoing clutch designs may be adapted to activate a roller traction or other drive system to selectively and automatically transfer torque to actuate drive means as required during operation of a drive system to drive an aircraft landing gear wheel to move the aircraft during taxi. Neither the foregoing clutch designs nor other commonly available clutch designs, moreover, are sufficiently robust to function effectively and reliably in an aircraft drive wheel drive system to engage a drive system to transfer torque as required to actuate a drive means and drive an aircraft autonomously during ground operations. Moreover, these systems do not provide the kind of failsafe capability that ensures that the clutch will never be engageable during flight, landing, takeoff, or during any other aircraft operating condition when operation of the drive wheel drive system would be unsafe.
A need exists, therefore, for a clutch assembly with the advantages of a selectable one-way clutch that is specifically designed as an integral component of an aircraft drive wheel drive system to automatically and selectively engage an aircraft drive wheel drive system and selectively transfer torque to actuate a highly efficient drive system-actuated non-engine drive means to drive an aircraft drive wheel and move the aircraft autonomously on the ground that also provides a failsafe capability ensuring that the clutch assembly will never be engageable to activate the drive system when aircraft operating conditions indicate that drive system operation is unsafe.